The Triumph of Unreason

　　A.

　　Neoclassical economics is built on the assumption that humans are rational beings who have a clear idea of their best interests and strive to extract maximum benefit (or “utility”， in economist-speak) from any situation. Neoclassical economics assumes that the process of decision-making is rational. But that contradicts growing evidence that decision-making draws on the emotions—even when reason is clearly involved.

　　B.

　　The role of emotions in decisions makes perfect sense. For situations met frequently in the past， such as obtaining food and mates， and confronting or fleeing from threats， the neural mechanisms required to weigh up the pros and cons will have been honed by evolution to produce an optimal outcome. Since emotion is the mechanism by which animals are prodded towards such outcomes， evolutionary and economic theory predict the same practical consequences for utility in these cases. But does this still apply when the ancestral machinery has to respond to the stimuli of urban modernity?

　　C.

　　One of the people who thinks that it does not is George Loewenstein， an economist at Carnegie Mellon University， in Pittsburgh. In particular， he suspects that modern shopping has subverted the decision-making machinery in a way that encourages people to run up debt. To prove the point he has teamed up with two psychologists， Brian Knutson of Stanford University and Drazen Prelec of the Massachusetts Institute of Technology， to look at what happens in the brain when it is deciding what to buy.

　　D.

　　In a study， the three researchers asked 26 volunteers to decide whether to buy a series of products such as a box of chocolates or a DVD of the television show that were flashed on a computer screen one after another. In each round of the task， the researchers first presented the product and then its price， with each step lasting four seconds. In the final stage， which also lasted four seconds， they asked the volunteers to make up their minds. While the volunteers were taking part in the experiment， the researchers scanned their brains using a technique called functional magnetic resonance imaging (fMRI)。 This measures blood flow and oxygen consumption in the brain， as an indication of its activity.

　　E.

　　The researchers found that different parts of the brain were involved at different stages of the test. The nucleus accumbens was the most active part when a product was being displayed. Moreover， the level of its activity correlated with the reported desirability of the product in question.